Measurement system and method for measuring an angle

ABSTRACT

The invention relates to a measurement system for measuring at least an angle of the first plane through a first surface area of an object. The system includes a sensor arrangement for measuring the coordinates in a measurement coordinate system of a plurality of measurement spots on the first surface area. The measurement system further includes an inclinometer for measuring an inclination of the measurement coordinate system to the direction opposite to the direction of the force of gravity. The measurement system also includes a processing device for determining the angle of the first plane based on the measured coordinates of the plurality of measurement spots, the measured inclination from the inclinometer and the direction opposite to the force of gravity. The system may also measure the angle of the second plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of InternationalApplication No. PCT/EP2013/069491 filed Sep. 19, 2013, and claimspriority to European Patent Application No. 12188434.0 filed Oct. 12,2012, the disclosures of which are hereby incorporated in their entiretyby reference.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a measurement system for measuring an anglebetween a first plane through a first surface area and a second planethrough a second surface area of an object, to a folding machine forfolding an object, to a method for measuring an angle between a firstplane through a first surface area, and a second plane through a secondsurface area of an object and to a method for folding a sheet.

Description of Related Art

EP1102032A1 describes a method for measuring a folding angle of a sheetin a folding machine. A rotationally supported scanner is used tomeasure the distance to the underside of a sheet in several rotationalpositions of the scanner. The scanner is also used to measure thedistance to an element of the folding machine in several rotationalpositions of the scanner. The measurements are performed in a planewhich is perpendicular to the longitudinal direction of the sheet andthe element.

Processing means determine a distance profile comprising the co-ordinatepoints for all the measured distances (to the sheet and to the elementof the folding machine). Two lines are fitted through the distanceprofile. The angle between the two lines is taken for the angle betweenthe sheet and the element. The folding angle is determined as 360degrees minus two times the angle between the sheet and the element.According to EP1102032A1 it is advantageous to avoid having to measurethe angle of the scanner with respect to the table on which the scannerand the element are mounted.

However, using a scanner to measure the distance to both the undersideof a sheet in several rotational positions of the scanner and theelement of the folding machine in several rotational positions of thescanner requires that both the underside and the element can be measuredwith the scanner. However, scanning the element requires time of thescanner which cannot be used to scan the underside of the sheet andtherefore reduces the throughput of the folding machine.

SUMMARY OF THE INVENTION

The object of the invention is to provide a measurement system and amethod to avoid this problem.

The object is reached by a measurement system for measuring an anglebetween a first plane through a first surface area and a second planethrough a second surface area of an object, comprising

-   -   a sensor arrangement for measuring the coordinates in a        measurement coordinate system of a plurality of measurement        spots in the first surface area, the plurality of measurement        spots comprising a first measurement spot at a first distance        from an intersection between the first plane and the second        plane and a second measurement spot at a second distance from        the intersection, the second distance differing from the first        distance;        -   characterised by    -   an inclinometer for measuring an inclination of the measurement        coordinate system to the direction opposite to the direction of        the force of gravity;    -   a processing device for determining the angle between the first        plane and the second plane based on the measured coordinates of        the plurality of measurement spots, the measured inclination and        information on the angle between the second plane and the        direction opposite to the force of gravity.

The measurement system according to the invention is used to measure theangle between a first plane through a first surface area and a secondplane through a second surface area on an object as a measure of theangle between the first surface area and the second surface area. In themeasurement system according to the invention the inclination providesinformation to link the measured coordinates in the measurementcoordinate system to the direction opposite to the force of gravity. Asthe second plane is not necessarily at the same angle to the directionopposite to the force of gravity, information on the angle between thesecond plane and the direction opposite to the force of gravity is usedto determine the angle between the first plane and the second plane.

The determination of the folding angle of a sheet is an example of thedetermination of the measurement of the angle between two planes runningalong the surfaces of the folded sheet. As the inclinometer providesinformation on the relation between the measurement coordinate systemand the direction opposite to the direction of the force of gravity,which is now taken as a reference, the sensor arrangement does notperform measurements on the element and, therefore, the angle can bedetermined faster.

In a further embodiment of the measurement system according to theinvention, the direction opposite to the force of gravity forms an axisof a reference coordinate system (X″Y″Z″) used by the inclinometer; andthe processing device is arranged

-   -   for determining the coordinates of the plurality of measurement        spots in the reference coordinate system based on the measured        inclination;    -   for estimating a specification of a line in the first plane        based on the coordinates of the plurality of measurement spots        in the reference coordinate system;    -   for projecting the line onto a plane perpendicular to the        intersection in an object coordinate system, the object        coordinate system comprising a Z-axis opposite to the direction        of the force of gravity;    -   for determining an angle between the Z-axis and the projection        of the line; and    -   for determining the angle between the first plane and the second        plane of the object based on the determined angle and        information on the angle between the second plane and the        direction opposite to the direction of the force of gravity.

According to the further embodiment the measured inclination providesinformation to be used by the processing means to perform atransformation of coordinate systems to determine the coordinates of themeasurement spots in the reference coordinate system. After estimating aspecification of the line in the reference coordinate system, the lineis projected onto a plane perpendicular to the intersection. Because thefirst and second measurement spot have a different distance to theintersection, the coordinates of the first and second measurement spotare sufficient to estimate a specification of a line in the first plane,the line not being parallel to the intersection. As the line is notparallel to the intersection, the angle between the Z-axis and theprojection of the line can be determined, and can be determined in asimple way because the Z-axis is part of the object coordinate system.Finally the processing means is used to determine the angle between thefirst surface area and the second surface area based on the determinedangle and information on the angle between the second plane and thedirection opposite to the direction of the force of gravity.

The further embodiment provides the advantage of a faster processingdevice, as coordinate transformations, estimating line specificationsand projections can be performed faster.

In a further embodiment of the measurement system according to theinvention, the sensor arrangement comprising a rotationally mountedscanner arranged to measure a coordinate of a first measurement spot ofthe plurality of measurement spots by sending measurement radiation in afirst measurement direction and to measure a second coordinate of asecond measurement spot by sending measurement radiation in a secondmeasurement direction.

As the scanner is rotationally mounted, it can send measurementradiation in different directions. By sending the measurement radiationin different directions, the coordinates of a plurality of measurementspots in the first surface area can be measured.

Rotating can be performed fast and accurately, which contributes to afast determination of the angle between the first plane and the secondplane.

In another embodiment, the measurement system according to the inventioncomprises

-   -   a further sensor arrangement for measuring the coordinates in a        further measurement coordinate system of a further plurality of        measurement spots in the second surface area, the further        plurality of measurement spots comprising a third measurement        spot at a third distance from the intersection and a fourth        measurement spot at a fourth distance from the intersection, the        fourth distance differing from the third distance;    -   a further inclinometer for measuring a further inclination of        the further measurement coordinate system to the direction        opposite to the direction of the force of gravity;    -   the processing means being further arranged to determine the        angle between the first plane and the second plane based on the        measured coordinates of the further measurement spots and the        measured further inclination.

According to this embodiment, the measurement system is arranged tomeasure the angle between the second plane and the direction opposite tothe direction of the force of gravity similar to the arrangement tomeasure the angle between the first plane and the direction opposite tothe direction of the force of gravity, which information is used todetermine the angle between the first plane and the second plane.According to the embodiment, the direction opposite to the direction ofthe force of gravity is taken as a reference and the angle between thesecond plane.

In a further embodiment of the measurement system according to theinvention, the direction opposite to the force of gravity forms an axisof a further reference coordinate system used by the furtherinclinometer. Also the processing means is further arranged

-   -   for determining the coordinates of the further plurality of        measurement spots in the further reference coordinate system        based on the measured further inclination;    -   for estimating a specification of a further line in the second        plane based on the coordinates of the further plurality of        measurement spots in the further reference coordinate system;    -   for projecting the further line onto a plane perpendicular to        the intersection in the object coordinate system;    -   for determining a further angle between the projection of the        further line and the Z-axis;    -   for determining the angle between the first plane and the second        plane of the object based on the determined angle and the        determined further angle.

According to the further embodiment the further inclination formsinformation to be used by the processing means to perform atransformation of coordinate systems to determine the coordinates of thefurther measurement spots in the further reference coordinate system.After estimating a specification of the further line in the furtherreference coordinate system, the further line is projected onto a planeperpendicular to the intersection. Because the third and fourthmeasurement spot have a different distance to the intersection, thecoordinates of the third and fourth measurement spot are sufficient toestimate a specification of a further line in the second plane, thefurther line not being parallel to the intersection. As the further lineis not parallel to the intersection, the angle between the Z-axis andthe projection of the line can be determined, and can be determined in asimple way because the Z-axis is part of the object coordinate system.Finally the processing means is used to determine the angle between thefirst surface area and the second surface area based on the determinedangle and information on the angle between the second plane and thedirection opposite to the direction of the force of gravity.

The further embodiment provides the advantage of simple requirements tothe processing device and being fast, as coordinate transformations,estimating line specifications and projections can be performed fast.

In yet a further embodiment, a folding machine for folding an objectcomprises a measurement arrangement according to the invention. Becausethe folding machine comprises a measurement arrangement according to theinvention, the object can be measured without having to remove theobject.

In a further embodiment the folding machine comprises an orientationsensor for measuring a first orientation of the measurement coordinatesystem with respect to compass directions; the processing means beingfurther arranged to use the measured first orientation and a storedvalue for a second orientation of a longitudinal direction of thefolding machine with respect to compass directions to determine thecoordinates of the plurality of measurement spots in the objectcoordinate system.

By measuring the first orientation with respect to compass directionsand a stored value for a second orientation of the longitudinaldirection of the folding machine, information on the direction of axisin the coordinate systems is be gathered. The processing means uses thisinformation for determining the coordinates of the measurement spots inthe object coordinate system. Therefore the folding machine requiresless calibration or less precise manufacturing to secure the alignmentof the object coordinate system with the measurement coordinate system.

In a further embodiment the folding machine comprises a firstorientation sensor for measuring a first orientation of the measurementcoordinate system with respect to compass directions and a secondorientation sensor for measuring the orientation of the objectcoordinate system with respect to compass directions, the processingmeans being further arrange to use the measured first orientation andthe measured second orientation sensor to determine the coordinates ofthe plurality of measurement spots in the object coordinate system.

By measuring the first orientation and second orientation with respectto compass directions information of the relative orientations betweenthe measurement coordinate system and the object coordinate system isobtained. This information is used by the processing means. This can beadvantageously used to position the measurement system at an unknownlocation and orientation with respect to the folding machine.

In an embodiment according to the invention, a method is provided formeasuring an angle between a first plane through a first surface areaand a second plane through a second surface area of an object, themethod comprising

-   -   using a sensor arrangement to measure coordinates in a        measurement coordinate system of a plurality of measurement        spots in the first surface area, the plurality of measurement        spots comprising a first measurement spot at a first distance        from an intersection between the first plane and the second        plane and a second measurement spot at a second distance from        the intersection, the second distance differing form the first        distance;    -   measuring an inclination of the measurement coordinate system to        the direction opposite to the force of gravity; and    -   determining the angle between the first plane and the second        plane based on the measured coordinates of the plurality of        measurement spots, the measured inclination and information on        the angle between the second plane and the direction opposite to        the force of gravity.

According to the method the angle between a first plane through a firstsurface area and a second plane through a second surface area on anobject is determined as a measure of the angle between the first surfacearea and the second surface area. In the method according to theinvention the inclination provides information to link the measuredcoordinates in the measurement coordinate system to the directionopposite to the force of gravity. As the second plane is not necessarilyat the same angle to the direction opposite to the force of gravity,information on the angle between the second plane and the directionopposite to the force of gravity is used to determine the angle betweenthe first plane and the second plane.

The determination of the folding angle of a sheet is an example of thedetermination of the measurement of the angle between two planes runningalong the surfaces of the folded sheet. As the inclinometer providesinformation on the relation between the measurement coordinate systemand the reference coordinate system, the sensor arrangement does notperform measurements on the element and therefore the angle can bedetermined faster.

In a further embodiment of the method, determining the angle between thefirst plane and the second plane based on the measured coordinates ofthe plurality of measurement spots, the measured inclination andinformation on the angle between the second plane and the direction ofthe force of gravity comprises

-   -   using the measured inclination to determine the coordinates of        the plurality of measurement spots in a reference coordinate        system of which the direction opposite to the force of gravity        forms an axis;    -   estimating a specification of a line in the first plane based on        the coordinates of the plurality of measurement spots in the        reference coordinate system;    -   projecting the line onto a plane perpendicular to the        intersection in an object coordinate system, the object        coordinate system comprising a Z-axis parallel to the direction        of the force of gravity;    -   determining an angle between the Z-axis and the projection of        the line; and    -   determining the angle between the first plane and the second        plane based on the determined angle and information on the angle        between the second plane and the direction of the force of        gravity.

According to the further embodiment the inclination forms information tobe used to perform a transformation of coordinate systems to determinethe coordinates of the measurement spots in the reference coordinatesystem. After estimating a specification of the line in the referencecoordinate system, the line is projected onto a plane perpendicular tothe intersection. Because the first and second measurement spot have adifferent distance to the intersection, the coordinates of the first andsecond measurement spot are sufficient to estimate a specification of aline in the first plane, the line not being parallel to theintersection. As the line is not parallel to the intersection, the anglebetween the Z-axis and the projection of the line can be determined, andcan be determined in a simple way because the Z-axis is part of theobject coordinate system. Finally the angle between the first surfacearea and the second surface area is determined based on the determinedangle and information on the angle between the second plane and thedirection opposite to the direction of the force of gravity.

The further embodiment of the method provides the advantage of simplerequirements to equipment for executing the method and being fast, ascoordinate transformations, estimating line specifications andprojections can be performed faster.

In a further embodiment of the invention, the method comprises

-   -   measuring a first orientation of the measurement coordinate        system with respect to compass directions;    -   determining the coordinates of the plurality of measurement        spots in the reference coordinate system based on the measured        first orientation and a stored value for a second orientation of        the intersection with respect to compass directions.

By measuring the first orientation with respect to compass directionsand a stored value for a second orientation on the intersection,information on the direction of axis in the coordinate systems aregathered. The processing means uses this information for determining thecoordinates of the measurement spots in the object coordinate system.Therefore this method can be applied with low restrictions oncalibration and less precise manufacturing to secure the alignment ofthe object coordinate system with the measurement coordinate system.

In a further method according to the invention, the method comprises

-   -   measuring the coordinates of the first measurement spot by        emitting measurement radiation in a first measurement direction;    -   using control means to rotate a scanner around an axis of the        measurement coordinate system;    -   measuring the coordinates of the second measurement spot by        emitting measurement radiation in a second measurement        direction; and    -   using information on the difference between the first        measurement direction and the second measurement direction for        determining the second inclination.

By rotating the scanner around, the measurement direction changes sothat the coordinates of several measurement spots in the plurality ofmeasurement spots can be measured. Rotating can be performed fast andaccurate.

In a further embodiment of the method according to the invention, themethod comprises

-   -   measuring the coordinates in a further measurement coordinate        system of a further plurality of measurement spots in the second        surface area, the further plurality of measurement spots        comprising a third measurement spot at a third distance from the        intersection and a fourth measurement spot at a fourth distance        from the intersection, the fourth distance differing from the        third distance;    -   measuring a further inclination of the further measurement        coordinate system to the direction opposite to the direction of        the force of gravity;    -   determining the angle between the first plane and the second        plane based on the measured coordinates of the further        measurement spots and the measured further inclination.

According to this embodiment, the measurement system is arranged tomeasure the angle between the second plane and the direction opposite tothe direction of the force of gravity similar to the arrangement tomeasure the angle between the first plane and the direction opposite tothe direction of the force of gravity, which information is used todetermine the angle between the first plane and the second plane.According to the embodiment, the direction opposite to the direction ofthe force of gravity is taken as a reference and the angle between thesecond plane. Therefore there is no need to measure the positions of anelement of a folding machine to determine this angle.

In a further embodiment of the invention, the step of determining theangle between the first plane and the second plane based on the measuredcoordinates of the further measurement spots and the measured furtherinclination comprises

-   -   determining the coordinates of the further plurality of        measurement spots in the further reference coordinate system        based on the measured further inclination;    -   estimating a specification of a further line in the second plane        based on the coordinates of the further plurality of measurement        spots;    -   projecting the further line onto a plane perpendicular to the        intersection in the object coordinate system;    -   determining a further angle between the projection of the        further line and the Z-axis; and    -   determining the angle between the first plane and the second        plane based on the determined angle and the determined further        angle.

According to the further embodiment the further inclination formsinformation to be used to perform a transformation of coordinate systemsto determine the coordinates of the further measurement spots in thefurther reference coordinate system. After estimating a specification ofthe further line in the further reference coordinate system, the furtherline is projected onto a plane perpendicular to the intersection.Because the third and fourth measurement spot have a different distanceto the intersection, the coordinates of the third and fourth measurementspot are sufficient to estimate a specification of a further line in thesecond plane, the further line not being parallel to the intersection.As the further line is not parallel to the intersection, the anglebetween the Z-axis and the projection of the line can be determined, andcan be determined in a simple way because the Z-axis is part of theobject coordinate system. Finally, the angle between the first surfacearea and the second surface area is determined based on the determinedangle and information on the angle between the second plane and thedirection opposite to the direction of the force of gravity.

The further embodiment provides the advantage of simple requirements tothe processing device and being fast, as coordinate transformations,estimating line specifications and projections can be performed fast.

In yet a further embodiment of the invention, the method comprisesfolding a sheet in a folding machine, determining the angle between thefirst plane and the second plane, and changing the angle between thefirst plane and the second plane by performing a further foldingoperation on the object in the folding machine.

The determined angle provides feedback on the angle between the firstplane and the second plane of the folded sheet. The angle is optimizedbased on this feedback in the further folding operation.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a side view of a sensor arrangement according to theinvention and a sheet supported on a folding machine

FIG. 2 shows the positions of a plurality of measurement spots in afirst surface area on the sheet

FIG. 3 shows a folding machine comprising a further sensor arrangement

FIG. 4 shows the positions of a further plurality of measurement spotsin a second surface area on the sheet

DETAILED DESCRIPTION OF THE INVENTION

In an embodiment of the invention, which is depicted in FIG. 1, afolding machine (54) comprises a measurement system (1). The foldingmachine (54) comprises a table (2) which comprises a key system (3) forfastening an element (4). The element (4) comprises a support die havinga recess (5) for supporting a sheet (6). The folding machine (54)further comprises a second element (7) comprising a moveable punch forfolding the sheet (6) in a known manner between the element (4) and thesecond element (7). The longitudinal direction (YY) (not shown) of theelement (4), the second element (7) and the recess (5) is in a directionperpendicular to the plane of the drawing.

The folding machine (54) further comprises a framework (8) forsupporting the table (2). This framework (8) also supports the drivesystem (not shown) for the second element (7). The drive systemcomprises a known adjustable hydraulic pressure device in order to foldthe sheet (6) to a desired folding angle.

In use, a sheet (6) is placed onto the element (4) and the secondelement (7) is driven towards the sheet (6) by the drive system (notshown). Accordingly the sheet (6) is driven into the recess by thesecond element (7), but as the sheet (6) is supported by the element(4), it bends along the longitudinal direction (XX). In the embodiment,the recess (5) and the second element (7) are symmetrical. The drivesystem is arranged to drive the second element along a drive directionparallel to the direction of the Z-axis of a Cartesian object coordinatesystem (X_(f)Y_(f)Z_(f)), whereby a movement of the second element (7)in the direction of the element (4) corresponds to a negative sign. Thefolding machine is leveled upon installation so that the drive directionand Z_(f)-direction are parallel to the direction of the force ofgravity. The Y_(f)-axis of the object coordinate system (XYZ) isparallel to the direction (YY) of the recess (5). In this embodiment therecess (5) is symmetrical around a plane of symmetry (indicated by adash dotted line), which comprises the Y_(f)-axis (or the longitudinaldirection of the recess (5)) and the Z_(f)-axis. The X_(f)-coordinate ofthe object coordinate system (X_(f)Y_(f)Z_(f)) is chosen to beperpendicular to the plane of symmetry of the recess (5). The secondelement (7) is arranged to be symmetrical around the plane of symmetry.With this arrangement, the fold in the sheet (6) is expected to besymmetrical around this plane of symmetry as well. Arranging the drivedirection to be parallel to the direction of the force of gravity andthe use of symmetry is advantageous to prevent the folding machine (54)to tilt or drift with respect to its surroundings while in use underinfluence of the large weight of the folding machine (54) and the largeforces used to fold for instance thick metal sheets (6). For the purposeof understanding the invention, also an object coordinate system (XYZ)is introduced, which in this embodiment is equal to the objectcoordinate system (X_(f)Y_(f)Z_(f)) apart from the position of theorigin. Thus, the direction of the X-axis is equal to the direction ofthe X_(f)-axis, the direction of the Y-axis is equal to the direction ofthe Y_(f)-axis and the direction of the Z-axis is equal to the directionof the Z_(f)-axis.

The folding machine (54) also comprises a measurement system (1) whichis supported by the framework (8). The measurement system comprises asensor (9), comprising a rotationally supported scanner (10). Thescanner (10) can measure and determine a distance between the scanner(10) and the sheet (6) by sending radiation to the object in ameasurement direction and receiving reflected radiation. For thispurpose the scanner (10) comprises a source of radiation. In thisembodiment a MEL Line Scanner M2D is used, which is a laser scanner forprofile contour scanning, marketed by Microelektronik GmbH,Eching/Germany. Alternative embodiments are based on other scannerswhich are for instance based on the sonar principle or, the principle oflaser triangulation.

The sensor (9) further comprises a control means (11) for controllingthe rotational position of the scanner (10) and thereby the measurementdirection. While keeping the relative locations and orientations of thesheet (6) and the measurement system (1) fixed, by changing themeasurement direction, the distance to different locations on the sheet(6) can be measured.

The measurement system (1) is mounted at a mounting angle (C) withrespect to the table (2) in such a way that the sensor (9) can measurethe distances in a plane which has the longitudinal direction (YY) asits normal, i.e. it is perpendicular to the longitudinal direction (YY).The sensor (9) is a two-dimensional sensor, which means that the scanner(10) is arranged to be rotated around one rotation axis. For aligningthe rotation axis to the longitudinal direction (YY), the measurementsystem (1) further comprises a mounting part (12) for mounting themeasurement system (1) to the framework (8). In an embodiment themounting part (12) comprises two references surfaces (13,14). They aresupported on two corresponding reference surfaces (15,16) on theframework (8). The corresponding reference surfaces (15,16) intersectalong a line that is parallel to the longitudinal direction (YY). As thecorresponding surfaces (15,16) support the reference surfaces (13,14),the reference surfaces (13,14) also intersect along a line that isparallel to the longitudinal direction (YY).

The sensor (9) is arranged to measure the value of a plurality ofdistances (D1, D2) between the sensor (9) and a plurality of measurementspots (S1,S2) on the side of the sheet (6) which faces the sensor (9).This is shown in FIG. 2. The different locations are in differentmeasurement directions from the origin of a Cartesian measurementcoordinate system (X′Y′Z′) of the sensor which coincides with the sourceof radiation of the scanner (10). The Y′-axis of the measurementcoordinate system (X′Y′Z′) is parallel to the longitudinal direction(YY). As the Y-axis of the object coordinate system (XYZ) is alsoparallel to the longitudinal direction (YY), the Y-axis and the Y′-axisare parallel. The X′-axis of the measurement coordinate system isparallel to the surface of the scanner (10) facing the sheet (6). In theembodiment a Cartesian coordinate system is used, but other coordinatesystems could be used as well. The Z′-axis of the measurement coordinatesystem extends from the scanner (10) in the direction of the sheet. Themeasurement directions correspond to measurement angles with the Z′-axisin the X′Z′-plane, as the scanner (10) is arranged to rotate around theY′-axis only. The origin of the measurement coordinate system (X′Y′Z′)is chosen such that the scanner rotates around the Y′-axis so as tofacilitate easier and thus faster processing later on.

The sensor (9) is arranged to transfer the measured values of theplurality of distances (D1,D2) and the corresponding measurement anglesto a processing device (18). The processing means is depicted in FIG. 1.The measured values and the corresponding measurement directions aretransferred via a wired connection (51). In an alternative embodimentthe measured values and the corresponding measurement directions aretransferred wirelessly, for instance via a Bluetooth or Wireless LAN(WLAN) connection. The measurement directions are transferred to theprocessing means (18) in the measurement coordinate system (X′Y′Z′) ofthe sensor.

The measurement system (1) further comprises an inclinometer (50) formeasuring a value of the inclination of the sensor (9) with respect tothe earth gravitational field, i.e. the direction of the force ofgravity. The inclinometer provides measurements in a Cartesian referencecoordinate system (X″Y″Z″). In this reference coordinate system(X″Y″Z″), the Z″-axis is parallel to the direction of the force ofgravity. However, a movement away from the center of gravity of theearth corresponds to a positive increase of the Z″-coordinate. Forsimplicity reasons, it is assumed here that the Y″-axis is parallel tothe longitudinal direction (XX), and therefore also parallel to thedirection of the Y′-axis of the measurement coordinate system. Withthese orientations of the Y″-axis and the Z″-axis, the X″-axis is in theX′Z′-plane of the measurement coordinate system. This is advantageous asthe transformations described below are simplest and can therefore beperformed fastest. The measured value of the inclination of the sensor(9) is also transferred to the processing means (18) in the referencecoordinate system (X″Y″Z″).

The processing means (18) are arranged to calculate the coordinates ofthe locations on the sheet (6) in the measurement coordinate system(X′Y′Z′) based on the values for the plurality of distances (D1, D2) andthe corresponding angles to the Z′-axis in the X′Z′-plane. It is to benoted that the X′Z′-plane coincides with the XZ-plane because the Y-axisand the Y′-axis are parallel and because both coordinate systems areCartesian. However, the coordinates of the plurality of measurementspots (S1,S2) differ in the XYZ-coordinate system and theX′Y′Z′-coordinate systems.

The processing means (18) are then used to perform a coordinatetransformation to express the coordinates of the plurality ofmeasurement spots on the sheet (6) in the reference coordinate system(X″Y″Z″). This is done based on the information that the Y′-axis andY″-axis are parallel to each other and the measured inclination of thesensor (9).

The processing means (18) is arranged to fit a straight line (21)through the calculated coordinates in the reference coordinate system(X″Y″Z″). This is advantageously done by using the least squarescriterion, as this is fastest and provides the best fit for the type ofmeasurement errors which are expected, i.e. normally distributedmeasurement errors. The fit corresponds to the following formula:X″=C1+αZ″wherein C1 represents an offset the value of which is not relevant. Asthe fold is parallel to the Y-axis of the object coordinate system, thenext step is to project the fit onto the XZ-plane, i.e. onto the planeperpendicular to the Y-axis. This means that the projection will beparallel to the Y-axis. Now because of the combination of facts thatZ-axis and Z″-axis are parallel, the Y-axis and the Y″-axis areparallel, the object coordinate system (XYZ) is Cartesian and thereference coordinate system (X″Y″Z″) is Cartesian, the X-axis and theX″-axis are parallel. However the origins of the object coordinatesystem (XYZ) and the reference coordinate system (X″Y″Z″) do notcoincide. Therefore, when projecting the fitted line onto XZ-plane, i.e.when projecting the fitted line parallel to the Y-axis, the line can berepresented asX=C2+αZwherein C2 represents an offset the value of which is not relevant. Theslope (α) of the line corresponds to the tangents of the angle betweenthe drive direction of the folding machine (54) and the sheet (6). Thisangle can therefore be calculated by calculating the arctangent of theslope of the line (a).

As the fold is expected to be symmetrical around the plane of symmetryand as this plane of symmetry comprises the drive direction and thus theZ-axis, the folding angle is now computed by the processing means (18),by multiplying the angle between the direction of the force of gravityand the sheet (6) by two.

The computed folding angle is transferred to a control system (53) via asecond wired connection (251) of the folding machine (54). The controlsystem compares the computed folding angle with a desired folding angleand controls the drive system to adjust the distance between the element(4) and the second element (7) to increase the folding area. Bycontinuously feeding computed folding angles to the control system (53)the desired folding angle of the sheet (6) can be accurately obtained.When the difference between the computed folding angle and the desiredfolding angle is below a threshold value, the control system (53)controls the drive system to increase the distance between the element(4) and the second element (7) so that the sheet (6) can be removed anda new sheet (6) can be placed in the folding machine (54).

In the embodiment described above, the scanner (10) is used to measure aplurality of distances (D1,D2) corresponding to a plurality ofmeasurement spots on the sheet (6). In an alternative embodiment,plurality of distances comprises a larger number of distances. Byincreasing the number of measured distances, the accuracy of the fit isincreased and therefore the accuracy of the computed folding angle. In afurther alternative embodiment, the scanner (10) is used to measure thedistance (D1) at least two times to increase accuracy of themeasurements.

In a further embodiment, the processing means (18) are integrated in thecontrol system (53) of the folding machine (54).

In a further embodiment, the scanner is not rotated around the Y′-axisof the measurement coordinate system (X′Y′Z′), but instead is moved bythe control means (11) in the X′-direction while maintaining the samemeasurement direction. As described earlier, a plurality of distances(D1,D2) is measured. The processing means (18) are arranged to calculatethe coordinates of the locations on the sheet (6) in the measurementcoordinate system (X′Y′Z′) based on the values for the plurality ofdistances (D1, D2), the corresponding angle between the measurementdirection and Z′-axis in the X′Z′-plane and the correspondingcoordinates of the scanner in the X′-direction. As before, theprocessing means (18) are further arranged to calculate the positions ofthe locations on the sheet (6) in the reference coordinate system(X″Y″Z″) based on the coordinates of the locations on the sheet (6) inthe measurement coordinate system (X′Y′Z′), the measured value of theinclination of the sensor (9) in the reference coordinate system(X″Y″Z″) and information on the relative orientations of the objectcoordinate system and the reference coordinate system. In an alternativeembodiment, the scanner (10) is moved in a combination of directions inthe measurement coordinate system, or a combination of movement androtation is applied. A limitation to helpful combinations can beunderstood by imagining a sheet coordinate system (RST) wherein theR-axis is parallel to the longitudinal direction of the fold. The T-axisis the normal to a first plane along a first surface of the sheet (6)where the measurement radiation is reflected. A second plane is situatedon the other side of the fold and along a second surface of the sheet(6). Both the first surface and the second surface face away from theplane of symmetry of the sheet (6). The first plane and the second planeintersect along an intersection line. The S-axis represents thedirection in which the distance of measurement spots to the intersectionline is measured. In order to be able to calculate the angle between thefirst plane and the driving direction (which lies in the plane ofsymmetry of the sheet (6), measurements at at least two differentS-coordinates (or two different distances from the intersection line)must be obtained. If only two measurements were obtained and both arefrom measurement spots at the same S-coordinate, the measurement spotswould have the same X and Z-coordinates in the object coordinate system.Having the same X- and Z-coordinates means that no line (21) can befitted through these points in the XZ-plane.

In an embodiment of the invention, the folding machine comprises afurther measurement system (1001) placed on the other side of the recess(5). This is shown in FIG. 3. The further measurement system (1001) andits elements have the same function as the measurement system (1) andthe corresponding elements, except for that it is arrange to measure atlocations of the sheet (6) on the other side of the recess and thereforeof the fold. It therefore comprises the similar elements such as afurther sensor (1009), a further scanner (1010) and a further controlmeans (1011) as well as a further wired connection (155) to theprocessing means (18). The further scanner (1010) is of the same type asthe scanner (10) and is rotated in a manner corresponding to therotation of scanner (10). The further measurement system (1001) ismounted at a further mounting angle (FC) with respect to the table (2)and comprises a further mounting part (1012) which comprises two furtherreference surfaces (1013,1014). The two further reference surfaces(1013, 1014) are supported on two further corresponding referencesurfaces (1015,1016) on the framework (8). The further correspondingreference surfaces (1015,1016) intersect along a line that is parallelto the longitudinal direction, i.e. the Y-axis of the object coordinatesystem.

The further sensor (1009) is arranged to measure the value of aplurality of further distances (D1001,D1002) between the further sensor(1009) and further measurement spots on the side of the sheet (6) whichfaces the further sensor (1009). The further measurement spots are in aplurality of further measurement directions from the origin of a furthermeasurement coordinate system (K′L′M′) of the sensor. This origin of thefurther measurement coordinate system (K′L′M′) coincides with the sourceof radiation of the further scanner (1010). The L′-axis of the furthermeasurement coordinate system (K′L′M′) is parallel to the longitudinaldirection (XX) and therefore is parallel to the Y′-axis around which thescanner (10) is rotated. The K′-axis of the further measurementcoordinate system is parallel to the surface of the further scanner(1010) facing the sheet (6). In the embodiment a Cartesian coordinatesystem is used, but other coordinate systems could be used as well. TheM′-axis of the measurement coordinate system extends from the furtherscanner (1010) in the direction of the sheet (6). The furthermeasurement directions correspond to further measurement angles with theM′-axis in the K′M′-plane, as the further scanner (1010) is arranged torotate around the L′-axis only. The origin of the measurement coordinatesystem (K′L′M′) is chosen such that the scanner rotates around theL′-axis so as to facility easier and thus faster processing later on.

The further sensor (1009) is arranged to transfer the measured values ofthe plurality of further distances (D1001,D1002) and the correspondingfurther measurement angles to the processing device (18) via a furtherwired connection (1051).

The further measurement system (1001) further comprises a furtherinclinometer (1050) for measuring a further value of the inclination ofthe further sensor (1009) with respect to the direction of the force ofgravity. The further inclinometer (1050) provides measurements in afurther reference coordinate system (K″L″M″). In this further referencecoordinate system (K″L″M″), the M″-axis is parallel to the direction ofthe force of gravity. For simplicity reasons, it is assumed here thatthe L″-axis is parallel to the longitudinal direction (XX), andtherefore also parallel to the direction of the Y′-axis and the Y″-axis.With these orientations the K″-axis is in the K′M′-plane of the furthermeasurement coordinate system. Also, with these orientations, and as thedirection of the force of gravity is equal when measured by theinclinometer (50) and the further inclinometer (1050), the furtherreference coordinate system (K″L″M″) coincides with the referencecoordinate system (X″Y″Z″) apart from a different position of thecorresponding origins. The further value of the inclination of thefurther sensor (1009) is transferred to the processing means (18) in thefurther reference coordinate system.

The processing means (18) is arranged to calculate the coordinates ofthe further measurement spots on the sheet (6) in a way similar to howit calculates the coordinates of the measurement spots. However, theprocessing means (18) calculates the coordinates of the furthermeasurement spots in the further measurement coordinate system (K′L′M′)based on the values of the plurality of further distances (D1001,D1002)and the corresponding further measurement angles of the correspondingfurther measurement directions to the M′-axis in the K′M′-plane. It isto be noted that the K′M′-plane is parallel to the XZ-plane because theY-axis and the L′-axis are parallel and because both coordinate systemsare Cartesian. However, the coordinates of a point in the K′M′-planediffer from the coordinates in the XZ-plane when projected onto theXZ-plane along the Y-axis.

The processing means (18) are then used to perform a coordinatetransformation to express the further coordinates of the furthermeasurement spots on the sheet (6) in the further reference coordinatesystem (K″L″M″). This is done based on the information that the L′-axisand the L″-axis are parallel to each other and the measured inclinationof the sensor (9).

The processing means (18) is arranged to fit a further straight line(1021) through the calculated coordinates in the further referencecoordinate system (K″L″M″) based upon the formulaK″=C3+βM″

This is done by using the least squares criterion for the same reasonsas for fitting the line (21). C3 represents a further offset the valueof which is not relevant. Now, because of the combination of facts thatthe Z-axis and M″-axis are parallel, the Y-axis and L″-axis areparallel, the object coordinate system is Cartesian and that the furtherreference coordinate system (K″L″M″) is Cartesian, the X-axis and theK″-axis are parallel. Even though the origins of the object coordinatesystem (XYZ) and the further reference coordinate system (K″L″M″) do notcoincide, the further straight line (1021) is represented in theXZ-plane asX=C4+βZ

The value of the offset C4 is not relevant. The further slope (β) of thefurther line (1021) corresponds to the tangents of the further anglebetween the drive direction of the folding machine (104) and the sheet(6). This further angle is calculated by the processing means (18) asthe arctangent of the further slope (β) of the further line (1021).

Note that both the angle and the further angle are angles to the Z-axisin the XZ-plane. Finally, the processing means (18) calculates thefolding angle by adding the angle and the further angle.

In an alternative embodiment the further scanner (1010) it is moved bythe further control means (1011) instead of being rotated, or acombination of rotation and movement is applied similar to what isforced onto the scanner (10). Alternatively the further control means(1011) and the control means are of a different type, or even apply adifferent measurement principle (sonar, laser triangulation) and aremoved or rotated in a different fashion.

In a further embodiment, the measurement system (1) comprises anorientation sensor (60) to determine the orientation of the measurementcoordinate system (X′Y′Z′) with respect to the earth magnetic field. Thefurther measurement system (1001) comprises a further orientation sensor(1060) to determine the orientation with respect to the earth magneticfield. The folding machine comprises a second orientation sensor (61).The measurements of the orientation sensor (60), the further orientationsensor (106) and the second orientation sensor (61) are used by theprocessing means (18) to verify the alignment of the different axis ofthe coordinate systems and to check if the orientations drift.

Alternatively, the measurement system (1) comprises an orientationsensor (60) for measuring the orientation of the measurement coordinatesystem (X′Y′Z′) with respect to compass directions. The folding machine(54) comprises a second orientation sensor (61) for measuring theorientation of the object coordinate system (XYZ) with respect tocompass directions. For this embodiment it is not relevant if a furthermeasurement system (1001) is present. In this embodiment, the Y′-axis ofthe measurement coordinate system (X′Y′Z′) is not parallel to thelongitudinal direction. The orientations measured by the orientationsensor (60) and the second orientation sensor (61) are used by theprocessing means (18) to make the suitable coordinate transformations.This is especially advantageous because the support of the measurementsystem (1) is less important. For instance the corresponding surfacescan intersect along any line. The measurement system (1) comprising anorientation sensor (60)) and the folding machine (54) comprising asecond orientation sensor is also advantageous to gain freedom toposition the measurement system (1) for instance in embodiments whereinthe measurement system (1) is not fixedly attached to the foldingmachine (54). Furthermore, based on the measured orientation of thecoordinate systems, the X′Z′plane, in which the measurements areperformed does not need to be perpendicular to the longitudinaldirection. Also, the coordinates of locations on the sheet (6) measuredwith a 3D-sensor can be calculated now and by suitable coordinatetransformations be used to calculate the folding angle.

In a further embodiment the measurement system (1) comprises an attitudeand heading reference system (AHRS) (70) which comprises theinclinometer (50) and the orientation sensor (60). The AHRS is alsoarranged to provide information on the acceleration. The measurementsystem (1) is moved along the frame (8), for instance over a rail, togather measurement data at a plurality of locations along thelongitudinal direction, i.e. at a plurality of Y-coordinates. Theaccelerations as measured by the AHRS (70) are integrated to give adisplacement. The displacement is transmitted to the processing means(18). The processing means use the displacement and the measurement dataat the plurality of locations along the longitudinal direction to fit aplane through the locations on the sheet (6) of which the distance ismeasured in this way. The processing means (18) are arranged to computethe angle between the fitted plane and Z′-axis and in an analoguefashion as described before to compute the folding angle based on theangle between the fitted plane and the Z′-axis by multiplying the angleby two.

In a further embodiment, a plurality of measurement systems (not shown)is positioned at different Y′-coordinates. The plurality of measurementsystems all provide information on the distance of the sheet (6) incorresponding measurement coordinate systems and the relation betweenthe measurement coordinate systems and the reference coordinate systemsas measured by inclinometers and orientations sensors comprised in theplurality of measurement systems. The information is combined to fit aplane through the locations on the sheet (6) and to compute an angle tothe direction of the force of gravity and finally the folding angle in away similar to what has been described above but with modificationswhich are clear to the person skilled in the art. While specificembodiments of the invention have been described above, it will beappreciated by a person of ordinary skill in the art that the inventionmay be practiced otherwise than as described, but still according to theteachings above. The descriptions above are intended to be illustrative,not limiting. For example, the invention may take the form of a computerprogram containing one or more sequences of machine-readableinstructions describing a method a disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein. Also, the element (4) may be driventowards and from the second element (7) or both may be driven towardsand from each other. Furthermore, the measurement system (1) comprisingthe inclinometer (50) and in some embodiments also the orientationsensor (60) may be supported by the element (4) or by the key system(3). Similarly, but independently the further measurement system (1001)comprising the further inclinometer (1050) may be supported by theelement (4) or by the key system (3). Furthermore, the processing meanscan be located elsewhere, for instance on the support table or on themeasurement system (1). As another example, the sensor may be tilted aswell to adjust the measurement direction. As yet another example,multiple sensors may be used, wherein each only measures the distance toone measurement spot as long as the measured coordinates of themeasurement spots can all be expressed in a single measurementcoordinate system. Hence the relationship between the measurementcoordinate systems of each sensor and the measurement directions shouldbe known. Also in practice different wordings may be used to mean thesame thing. For instance, the folding machines can also be referred toas press brakes.

The invention claimed is:
 1. For an object having a first plane with afirst surface area facing away from a plane of symmetry, said plane ofsymmetry being centrally arranged within a folding machine and isparallel to a drive direction of a first element and a second element ofsaid folding machine, said elements being arranged about said plane ofsymmetry and are driven to impart a force upon the object to form anexpected fold around said plane of symmetry and an adjacent second planewith a second surface area facing away from the plane of symmetry with anon-zero angle formed between the first plane and the second plane alongthe plane of symmetry, a measurement system is for measuring at least anangle of the first plane, comprising: a sensor arrangement comprising afixed sensor, fixedly mounted to the folding machine on a framework in arelative location and orientation between the object and the measurementsystem by a mounting part, said fixed sensor for measuring thecoordinates in a measurement coordinate system of a plurality ofmeasurement spots on the first surface area, the plurality ofmeasurement spots comprising a first measurement spot at a firstdistance from an intersection between the first plane and the secondplane along the plane of symmetry and a second measurement spot at asecond distance from the intersection along the plane of symmetry, thesecond distance differing from the first distance and wherein the fixedsensor arrangement further comprises a rotationally supported scannerrotationally mounted inside the fixed sensor to support severalrotational positions of the scanner, the rotationally supported scannerbeing arranged to measure a coordinate of a first measurement spot ofthe plurality of measurement spots by sending measurement radiation in afirst measurement direction at a first rotational position of therotationally supported scanner and to measure a second coordinate of asecond measurement spot by sending measurement radiation in a secondmeasurement direction at a second rotational position of therotationally supported scanner; an inclinometer for measuring aninclination of the measurement coordinate system relative to thedirection opposite to the direction of the force of gravity, wherein theinclinometer determines the direction of gravity used for themeasurement; and a processing device for determining the angle of thefirst plane based on the measured coordinates of the plurality ofmeasurement spots, the measured inclination from the inclinometer andthe direction opposite to the force of gravity.
 2. The measurementsystem according to claim 1, wherein the direction opposite to the forceof gravity is used to form an axis of a reference coordinate systemrelative to the measurement coordinate system used by the inclinometer;and wherein the processing device is used: for determining thecoordinates of the plurality of measurement spots in the referencecoordinate system based upon the measured inclination; for estimating aspecification of a line in the first plane based on the coordinates ofthe plurality of measurement spots in the reference coordinate system;for projecting the line onto a plane perpendicular to the intersectionin an object coordinate system, the object coordinate system comprisinga Z-axis opposite to the direction of the force of gravity; fordetermining an angle between the Z-axis and the projection of the line;and for determining the angle of the first plane of the object based onthe determined angle and the direction opposite to the direction of theforce of gravity.
 3. The measurement system according to claim 1,further comprising; a further fixed sensor arrangement, fixedly mountedto the folding machine on the framework in a relative location andorientation between the object and the measurement system by a mountingpart on the opposite side of the plane of symmetry from theaforementioned fixed sensor arrangement, the further fixed sensorarrangement for measuring the coordinates in a further measurementcoordinate system of a further plurality of measurement spots in thesecond surface area, the further plurality of measurement spotscomprising a third measurement spot at a third distance from theintersection along the plane of symmetry and a fourth measurement spotat a fourth distance from the intersection along the plane of symmetry,the fourth distance differing from the third distance; and a furtherinclinometer for measuring a further inclination of the furthermeasurement coordinate system to the direction opposite to the directionof the force of gravity; the processing means being further arranged todetermine the angle of the second plane based on the measuredcoordinates of the further measurement spots and the measured furtherinclination.
 4. The measurement system according to claim 3, wherein thedirection opposite to the force of gravity forms an axis of a furtherreference coordinate system used by the further inclinometer; andwherein the processing means is further used: for determining thecoordinates of the further plurality of measurement spots in the furtherreference coordinate system based on the measured further inclination;for estimating a specification of a further line in the second planebased on the coordinates of the further plurality of measurement spotsin the further reference coordinate system; for projecting the furtherline onto a plane perpendicular to the intersection in an objectcoordinate system; for determining a further angle between theprojection of the further line and a Z-axis opposite to the direction ofthe force of gravity; and for determining the angle of the second planeof the object based on the determined angle and the determined furtherangle.
 5. For an object having a first plane with a first surface areafacing away from a plane of symmetry, said plane of symmetry beingcentrally arranged within a folding machine and is parallel to a drivesection of a first element and a second element of said folding machine,said elements being arranged about said plane of symmetry and are drivento impart a force upon the object to form an expected fold around saidplane of symmetry and an adjacent second plane with a second surfacearea facing away from the plane of symmetry with a non-zero angle formedbetween the first plane and the second plane along the plane ofsymmetry, a measurement system is for measuring at least an angle of thefirst plane, comprising: a sensor arrangement comprising a fixed sensor,fixedly mounted to the folding machine on a framework in a relativelocation and orientation between the object and the measurement systemby a mounting part, the fixed sensor for measuring the coordinates in ameasurement coordinate system of a plurality of measurement spots on thefirst surface area, the plurality of measurement spots comprising afirst measurement spot at a first distance from an intersection betweenthe first plane and the second plane along the plane of symmetry and asecond measurement spot at a second distance from the intersection, thesecond distance differing from the first distance; and wherein the fixedsensor arrangement further comprises a rotationally supported scannerrotationally mounted inside of the fixed sensor to support severalrotational positions of the scanner, the rotationally supported scannerbeing arranged to measure a coordinate of a first measurement spot ofthe plurality of measurement spots by sending measurement radiation in afirst measurement direction at a first rotational position of therotationally supported scanner and to measure a second coordinate of asecond measurement spot by sending measurement radiation in a secondmeasurement direction at a second rotational position of therotationally supported scanner; an inclinometer for measuring aninclination of the measurement coordinate system relative to thedirection opposite to the direction of the force of gravity, wherein theinclinometer determines the direction of gravity used for themeasurement; a processing device for determining the angle of the firstplane based on the measured coordinates of the plurality of measurementspots, the measured inclination from the inclinometer and the directionopposite to the force of gravity and a further fixed sensor arrangement,fixedly mounted to the folding machine on the framework in a relativelocation and orientation between the object and the measurement systemon the opposite side of the plane of symmetry from the aforementionedfixed sensor arrangement by a mounting part, the further fixed sensorarrangement for measuring the coordinates in a further measurementcoordinate system of a further plurality of measurement spots in thesecond surface area, the further plurality of measurement spotscomprising a third measurement spot at a third distance from theintersection along the plane of symmetry and a fourth measurement spotat a fourth distance from the intersection along the plane of symmetry,the fourth distance differing from the third distance; a furtherinclinometer for measuring a further inclination of the furthermeasurement coordinate system to the direction opposite to the directionof the force of gravity; and the processing means being further arrangedto determine the angle of the second plane based on the measuredcoordinates of the further measurement spots and the measured furtherinclination.